Convergent/divergent segmented exhaust nozzle

ABSTRACT

A segmented exhaust nozzle for attenuating noise from a turbofan jet engine without adversely impacting the operability or operability limit related performance of the engine. The exhaust nozzle includes spaced apart fan nozzle inner and outer walls which form an annular exhaust gas flow path therebetween. The fan nozzle outer wall is segmented at the downstream end. The outer wall curves inwardly towards the inner wall and then turns back away from the inner wall to form an arcuate protrusion that extends into the exhaust gas flow path forming an aerodynamic throat. Through the segmented portion of the nozzle, the outer wall then continues to curve away from the inner wall before again curving back towards the inner wall at a nozzle exit station. The nozzle exit effective area is approximately equal in cross sectional area to a conventional exhaust nozzle exit area. The inwardly curving and then segmented outwardly curving portion of the exhaust nozzle forms a geometric influction that serves to reduce noise without negatively affecting engine operability or operability limit related performance.

FIELD OF THE INVENTION

[0001] This invention relates to exhaust nozzles used with turbofanengines, and more particularly to an exhaust nozzle used with a turbofanjet engine for reducing the noise of the exhaust gasses emitted from theengine without suppressing the flow of exhaust gasses through theexhaust nozzle.

BACKGROUND OF THE INVENTION

[0002] The reduction of exhaust flow jet noise from turbofan aircraftengines is essential to meeting current and anticipated futuregovernment regulatory requirements for Airplane Type Certification, aswell as numerous local airport noise ordinances. There have been manyattempts to accomplish jet exhaust noise reduction through variousmodifications to the exhaust nozzle of the engine. While many of theseattempts have produced some degree of noise reduction, they have alsoresulted in adverse impacts on engine operability and/or engineoperability limit related performance.

[0003] A jet noise reducing nozzle segment is typically triangular inplanform and is contoured to increasingly immerse or extend into theexhaust flow with distance along its length. Multiple segments attachedto the exit of a conventional exhaust nozzle are typically used to forma jet noise reducing segmented exhaust nozzle. The effective flow areaof the exhaust nozzle is reduced when nozzle segments are employed dueto the presence of portions of the nozzle segment projecting into theexhaust gas flow path. These portions, in effect, present additionalblockage to the oncoming exhaust gas flow. On a turbofan engine, theadditional blockage results in reduced fan flutter margin which cannegatively impact fan aero-elastic structural stability. It also cancause increased exhaust gas temperatures which can negatively impactturbine life. Still further, it can result in reduced engine compressorstall margin which can negatively impact engine core operationstability. Individually or together, these impacts can be of suchsignificance that they prevent the implementation of the noise-reducingdevice on a jet engine. This impact is particularly hard felt on olderjet engine designs that have been “thrust bumped” to near theiroperational limits.

[0004] With ever increasing stringency of new community noiselimitations, existing aircraft types currently in service, as well asnew designs for future aircraft, will require new jet noise controltechnology. This increased stringency could potentially present a threatto the introduction of future aircraft designs. Moreover, ever strictercommunity noise limitations, if not addressed by suitable noisereduction technology, could impede the introduction of derivativeaircraft platforms.

[0005] Accordingly, there exists a need to further reduce the noiseproduced by turbofan jet aircraft engines without imposing anunacceptable reduction in engine operability margins or operabilitylimit related performance.

SUMMARY OF THE INVENTION

[0006] The present invention is directed to a segmented exhaust nozzlethat effectively reduces the exhaust jet noise generated by a turbofanjet aircraft engine without adversely impacting engine operability oroperability limit related performance. The exhaust nozzle is formed by afan inner wall and a fan outer wall. The inner and outer wallscooperatively form an annular exhaust gas flow path therebetween. Thewalls further define a nozzle throat area and a nozzle exit area fromwhich the exhaust gasses of a turbofan engine associated with theexhaust nozzle are emitted.

[0007] The exhaust nozzle of the present invention provides a firstregion in which one of the inner or outer walls curves gradually towardsthe other, thereby presenting reduced cross-sectional area to exhaustgas flow in this region forming an aerodynamic throat. A second region,through the segmented portion of the nozzle and downstream of the firstregion, is formed by the one wall curving away from the other wall toproduce a region of increased cross-sectional area to exhaust gas flow.Importantly, the second region forms an exhaust gas nozzle exit areawhich has an effective cross sectional area approximately equal to aconventional exhaust gas nozzle exit area. This is in contrast topreviously developed, segmented exhaust nozzles in which the exhaust gasnozzle exit area is smaller in cross section than a conventional exhaustnozzle exit area. This difference effectively serves to eliminate thenegative impact on engine operability and operability limit relatedperformance introduced by previous segmented exhaust nozzleconfigurations while still providing a significant reduction in enginejet noise.

[0008] The present invention thus reduces significantly the exhaust gasflow suppression that would typically be present with previous forms ofsegmented exhaust nozzles by presenting a geometric inflection throughthe flow control region of the nozzle. The inflective profile creates aconversion-divergent, cross sectional shape to the nozzle wall. Theresult is a net zero change in exhaust flow characteristic and a netzero change in segmented nozzle noise suppression effectiveness.

[0009] Further areas of applicability of the present invention willbecome apparent from the detailed description provided hereinafter. Itshould be understood that the detailed description and specificexamples, while indicating the preferred embodiment of the invention,are intended for purposes of illustration only and are not intended tolimited the scope of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

[0010] The present invention will become more fully understood from thedetailed description and the accompanying drawings, wherein:

[0011]FIG. 1 is a highly simplified side view of an exhaust nozzle inaccordance with a preferred embodiment of the present invention;

[0012]FIG. 2 is a highly simplified cross sectional view of a portion ofan exhaust nozzle in accordance with section line 2-2 in FIG. 1illustrating the curvature of the convergent/divergent segmented exhaustnozzle of the present invention;

[0013]FIG. 3 is a bar graph illustrating test results for noisereduction under various operating conditions;

[0014]FIG. 4 is a graph illustrating the overall sound pressure levelrelative to a body station of an aircraft; and

[0015]FIG. 5 is a graph illustrating the nozzle discharge characteristicof the segmented exhaust nozzle of the present invention as compared tothat of a conventional exhaust nozzle flow characteristic and the flowcharacteristic of previous designed segmented nozzles.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0016] The following description of the preferred embodiment(s) ismerely exemplary in nature and is in no way intended to limit theinvention, its application, or uses.

[0017] Referring to FIG. 1, there is shown a segmented exhaust nozzle 10in accordance with a preferred embodiment of the present invention. Theexhaust nozzle 10 is particularly adapted for use with high bypass ratioturbofan jet engines. In this example, an external plug 11 is disposedwithin a housing structure forming a nacelle 18 along an imaginary axialcenter line “C_(L)” of the nacelle.

[0018] Referring to FIG. 2, there is shown a portion of the segmentedexhaust nozzle 10. The segmented exhaust nozzle 10 includes a fan nozzleinner wall 12 and a fan nozzle outer wall 14 spaced apart from the innerwall 12. Cooperatively, the walls 12 and 14 form an annular exhaust gasflow path 16. The exhaust nozzle 10 is further typically containedwithin the nacelle 18, which also houses the turbofan jet engine (notshown).

[0019] The outer wall 14 of the segmented exhaust nozzle 10 comprises aunique contour which effectively serves to reduce the exhaust jet noisegenerated by the turbofan jet engine without negatively impacting theoperability or operability limit related performance of the engine. Theouter wall 14 includes a portion curving gradually inwardly toward theinner wall 12 from a first point 20 to a second point 22 forming anaerodynamic choke point. From point 22, the outer wall 14 changesdirection and curves gradually away from the inner wall 12 to a thirdpoint 24. Thereafter, the outer wall 14 again begins to curve towardsthe inner wall 12 to a fourth point 26. This is the segmented region ofthe nozzle. Point 22 also defines the location of the exhaust nozzlethroat area (“A_(throat)”) while an integration of points 24 through 26comprises the segmented exhaust nozzle exit area (“A_(exit)”). Forcomparison purposes, “A_(E1)” defines a point at which a conventionalexhaust nozzle exit area would be located. Also, “A_(E1) through A_(E2)”defines an exhaust nozzle exit area for a previously developed, typicalsegmented exhaust nozzle.

[0020] From FIG. 2 it can be seen that points 20-24 define a firstregion in which the outer wall 14 forms an arcuate protrusion whichprojects into the exhaust gas flow path 16. The axial distance betweenpoints 24 and 26 defines a region of increased cross-sectional area tothe exhaust gas flow. It will also be appreciated that the edge ofregion two, points 24 through 26, provides an effective cross sectionalarea, represented by the imaginary line 26, which is approximately equalto A_(E1), but still larger than A_(E2). The entire wall structurebetween points 20 and 26 can be viewed as forming a geometric inflectionin the exhaust gas flow path 16. The area between points 22 and 24presents an increased cross-sectional area to the exhaust gas flow,thereby reducing blockage. The subsequent curvature back towards theinner wall 12 serves to realign the flow of exhaust gasses to maximizethe nozzle noise reduction efficiency. The result is a segmented nozzlewith distinct sonic and subsonic flow control regions yielding a netzero change in flow characteristic and a net zero change in segmentnoise suppression effectiveness of the segmented exhaust nozzle 10.

[0021] While it will be appreciated that the outer wall 14 of theexhaust nozzle 10 has been illustrated as including the geometricinfluction surface, it will be appreciated that this surface could alsobe provided on the inner wall 12 of the exhaust nozzle 10.

[0022] Referring to FIG. 3, a graph 30 illustrates the reduction inexhaust gas flow noise with the segmented exhaust nozzle 10 of thepresent invention during a flight test.

[0023]FIG. 4 is a graph 32 illustrating the reduction in interior noiseof an aircraft incorporating the segmented exhaust nozzle 10 of thepresent invention.

[0024]FIG. 5 illustrates a graph 32 of the flow characteristic of thesegmented exhaust nozzle 10 of the present invention as compared to aconventional exhaust nozzle flow 34 and a flow characteristic of apreviously developed, segmented nozzle design 36. From FIG. 5 it will beappreciated that the flow characteristics of the exhaust nozzle 10closely match those of a conventional exhaust nozzle.

[0025] It will be appreciated then that the segmented exhaust nozzle 10of the present invention provides a means to significantly attenuate theexhaust jet noise produced by turbofan engines, and thus help to meetincreasingly stringent community noise requirements. Importantly, theexhaust nozzle 10 does not adversely impact the operation or operabilitylimit related performance of existing large turbofan jet engines.

[0026] The segmented exhaust nozzle 10 is further capable of being usedas a segmented nozzle in exhaust nozzles having an internal primaryplug, such that no inner wall is present. In such an exhaust nozzle, theouter wall 14 would curve with reference to the imaginary center lineC_(L), since no inner wall would be present.

[0027] Those skilled in the art can now appreciate from the foregoingdescription that the broad teachings of the present invention can beimplemented in a variety of forms. Therefore, while this invention hasbeen described in connection with particular examples thereof, the truescope of the invention should not be so limited since othermodifications will become apparent to the skilled practitioner upon astudy of the drawings, specification and following claims.

What is claimed is:
 1. A segmented exhaust nozzle for use with aturbofan engine to inhibit jet exhaust noise emitted from the turbofanengine, said exhaust nozzle comprising: a circumferential fan nozzleinner wall; a circumferential fan nozzle outer wall spaced apart fromsaid inner wall to define an annular exhaust gas flow path therebetween;one of said inner and outer walls curving toward the other to define aprotrusion, at a first region of said exhaust gas flow path, whichextends into said exhaust gas flow path to reduce a cross sectional areaof said exhaust gas flow path forming a choke flow control region; saidone wall gradually curving away from the other, and then back toward theother, to define a second region downstream of said first region forproviding first an increasing and then a decreasing cross sectional areain a direction of said exhaust gas flow providing increasedcross-sectional area for un-choked flow control; and a downstream edgeof said second region defining a nozzle exit area having an effectivecross sectional area approximately equal to a conventional exhaustnozzle exit area.
 2. The exhaust nozzle of claim 1, wherein a midpointof said second region defines a cross sectional area which is largerthan said conventional nozzle exit area.
 3. The exhaust nozzle of claim1, wherein said exhaust nozzle forms an extension of an existing exhaustgas nozzle structure.
 4. A segmented exhaust nozzle for use with aturbofan engine to inhibit exhaust jet noise emitted from the turbofanengine, said exhaust nozzle comprising: a circumferential fan nozzleinner wall; a circumferential fan nozzle outer wall spaced apart fromsaid inner wall to define an annular exhaust gas flow path therebetween;said outer wall curving toward the inner wall to define an arcuateprotrusion, at a first region of said exhaust gas flow path, whichextends into said exhaust gas flow path to reduce a cross sectional areaof said exhaust gas flow path and thereby provide a choke flow controlregion along the exhaust gas flow path; said outer wall graduallycurving away from the inner wall, and then back toward the inner wall,to define a region downstream of said arcuate protrusion for providingincreased cross-sectional area for un-choked flow control to saidexhaust gas flowing through said exhaust gas flow path, said regionhaving first an increasing and then a decreasing cross sectional area ina direction of said exhaust gas flow; and an edge of said downstreamregion defining a nozzle exit having an effective cross sectional areaapproximately equal to a conventional exhaust nozzle exit area.
 5. Theexhaust nozzle of claim 4, wherein a midpoint of said region defines alarger cross sectional area than said edge of said region.
 6. Theexhaust nozzle of claim 5, wherein said midpoint defines a larger crosssectional area of said conventional exhaust nozzle exit area.
 7. Asegmented exhaust nozzle for use with a turbofan engine fan exhaustnozzle structure, said exhaust nozzle comprising: a fan nozzle innerwall; a fan nozzle outer wall spaced apart from said fan nozzle innerwall; said inner and outer walls forming said exhaust nozzle and havinga nozzle throat area and a nozzle exit area downstream from said nozzlethroat area; at least one of said inner and outer walls curvinggradually toward the other from a first point to a second pointpositioned downstream of said first point, relative to exhaust gas flowthrough said nozzle, to thereby reduce a cross sectional area of anozzle forming an aerodynamic throat area of said exhaust nozzle; saidat least one of said walls then curving gradually away from the otherfrom said second point to a third point downstream of said second point,relative to said exhaust gas flow, to thereby effectively increase thecross section area presented to the flow within said exhaust nozzle, andwherein an intermediate point between said second and third pointsdefines where a conventional nozzle exit point is located on aconventional exhaust nozzle; said at least one of said walls thencurving gradually toward the other from said third point to a fourthpoint downstream of said third point, relative to said exhaust gas flow,to thereby reduce a cross sectional distance between the walls withinsaid exhaust nozzle at said fourth point; and wherein said crosssectional area integrated between said third point and said fourth pointis substantially equal to a cross section area at said intermediatepoint.
 8. The exhaust nozzle of claim 7, wherein a region between saidfirst and second points represents an arcuate protrusion to acceleratesaid exhaust gas flow.
 9. The exhaust nozzle of claim 7, wherein aregion between said second and fourth points presents increased crosssectional area for subsonic exhaust gas flow control.
 10. A segmentedexhaust nozzle for use with a turbofan engine fan exhaust nozzlestructure, said exhaust nozzle comprising: a fan nozzle inner wall; afan nozzle outer wall spaced apart from said fan nozzle inner wall toform an annular exhaust gas flow path; said exhaust nozzle having anozzle throat area and a nozzle exit area downstream from said nozzlethroat area; said outer wall curving gradually toward the inner wallfrom a first point to a second point positioned downstream of said firstpoint, relative to exhaust gas flow through said nozzle, to therebyreduce nozzle throat cross sectional area of said exhaust nozzle andaccelerate said exhaust gas flow therethrough; said outer wall thencurving gradually away from the inner wall from said second point to athird point downstream of said second point, relative to said exhaustgas flow, to thereby effectively increase the cross sectional areapresented to said exhaust gas flow within said exhaust nozzle wherein anintermediate point between said second and third points defines where aconventional nozzle exit point is located on a conventional exhaustnozzle; and said outer wall then curving gradually toward the inner wallfrom said third point to a fourth point downstream of said third point,relative to said exhaust gas flow, to thereby reduce the cross sectionaldistance between the inner and outer walls at said fourth point; andwherein said cross sectional area integrated through said third pointand said fourth point is substantially equal to a cross section area atsaid intermediate point.
 11. The exhaust nozzle of claim 10, wherein aregion between said first and third points defines an arcuateprotrusion.
 12. A segmented exhaust nozzle for use with a turbofanengine to inhibit jet exhaust noise emitted from the turbofan engine,said exhaust nozzle comprising: a circumferential fan nozzle outer wallspaced apart from an imaginary axial center line of said nozzle; saidouter wall curving toward said imaginary axial center line to define aprotrusion, at a first region of said exhaust gas flow path, whichextends into said exhaust gas flow path to reduce a cross sectional areaof said exhaust gas flow path forming a choke flow control region; saidouter wall gradually curving away from said imaginary axial center line,and then back toward said center line, to define a second regiondownstream of said first region for providing first an increasing andthen a decreasing cross sectional area in a direction of said exhaustgas flow providing increased cross-sectional area for un-choked flowcontrol; and a downstream edge of said second region defining a nozzleexit area having an effective cross sectional area approximately equalto a conventional exhaust nozzle exit area.